JP5361235B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Abstract

A sheet conveying apparatus for conveying a sheet having an image formed thereon includes: a first rotator; a second rotator that comes into pressure contact with the first rotator and contacts a surface of the sheet having the image formed thereon; and a plurality of ribs that are formed on a circumferential surface of the second rotator and disposed in an axial direction so as to be continuous in a circumferential direction. Among the plurality of ribs, the ribs disposed at both ends of the second rotator in the axial direction have a diameter that is smaller than those of the other ribs.

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to a configuration for preventing deterioration in image quality when conveying a sheet.

  In conventional image forming apparatuses such as copiers, printers, and facsimile machines, a toner image formed on a photosensitive drum, which is an image carrier provided in an image forming unit, is transferred to a sheet, and then the sheet is used as a fixing device. I am trying to carry it. In this fixing device, the sheet is heated and pressed to fix the toner image on the sheet, and then the sheet having the toner image fixed thereon is conveyed by the sheet conveying device to be discharged to the sheet discharge stacking unit. ing.

  By the way, in the conventional image forming apparatus, if the roller or the like comes into contact with the toner image forming surface or the back surface of the sheet before the toner image heated and fixed at high temperature is completely cooled, the surface property of the contact portion may be changed. Part is deprived of heat earlier than other parts. As a result, the color of the toner image is changed, so that a so-called roller mark that is visually recognized as a gloss difference is generated, and the image quality is lowered. The roller marks are not noticeable on plain paper, but are easily noticeable on high gloss sheets such as projector sheets, glossy paper, and glossy films.

  Therefore, in order to prevent the deterioration of image quality due to the occurrence of such roller marks, for example, a heat-insulating roller is used as a conveyance roller (discharge roller) of a sheet conveyance device that contacts a toner image heated and fixed at a high temperature. (See Patent Document 1).

  FIG. 10A shows the configuration of a roller having such heat insulation properties. This roller includes a heat insulating layer 101 formed on the circumferential surface of the metal shaft 100, an uneven shape 102 formed on the heat insulating layer 101, and a surface protective layer formed on the circumferential surface of the heat insulating layer 101. 103.

  In order to prevent deterioration in image quality due to the occurrence of roller marks, for example, a roller having a small contact area with a sheet is used as a roller of a sheet conveying device that comes into contact with a toner image heated and fixed at a high temperature. (See Patent Document 2).

  FIG. 10B shows the structure of such a roller, and this roller 110 is provided with a plurality of minute protrusions 110a on the outer peripheral surface that comes into contact with the heat-fixed toner image. By providing such minute protrusions 110a, the toner on the sheet and the roller are brought into point contact before the toner image is completely cooled, thereby preventing the generation of a roller mark.

JP 2004-301291 A JP 2006-145586 A

  However, in the conventional sheet conveying apparatus using the roller having heat insulation described above, the cost of the roller (heat insulating roller) increases because the cost of the material for forming the heat insulating layer is high. In addition, since the hardness of the heat insulator constituting the heat insulator layer is low, when a roller or the like is pressed against the roller, the heat insulator layer is compressed and the heat insulation effect is reduced, resulting in roller marks and image The quality is lowered. In order to prevent a decrease in the heat insulation effect, if the biasing force of the spring that generates the pressing force such as the roller that is in pressure contact with the roller is weakened, the conveying force (discharge force) of the roller pair will decrease, and The sheet cannot be discharged.

  Further, in a conventional sheet conveying apparatus using a discharge roller having a plurality of minute protrusions on the outer peripheral surface, the releasability from the toner may deteriorate due to the plurality of minute protrusions on the outer peripheral surface of the roller. Here, when the releasability from the toner is deteriorated as described above, the toner on the sheet is peeled off when the sheet passes the roller pair before the heat-fixed toner image is completely cooled. Image quality deteriorates. Further, the toner that has been peeled off may adhere to the roller.

  In addition, when the contact area between the toner and the roller is reduced by forming minute protrusions on the outer peripheral surface of the roller, if the height of the contact portion of the minute protrusions with the sheet becomes non-uniform, it is locally High pressure may be applied. As a result, the toner on the sheet is peeled off, or the sheet is deformed to cause unevenness on the sheet, resulting in a decrease in image quality.

  Here, in order to prevent the toner that has been peeled off from adhering to the roller, it is conceivable to form a surface protective layer on the circumferential surface of the roller. The protrusion on the outer peripheral surface becomes smooth. As a result, the contact area between the toner on the sheet and the roller increases, and the generation of roller marks cannot be sufficiently suppressed.

  Accordingly, the present invention has been made in view of such a current situation, and provides a sheet conveying apparatus and an image forming apparatus that can convey a sheet reliably at low cost and without reducing image quality. It is for the purpose.

According to the present invention, in a sheet conveying apparatus that conveys a sheet on which an image is formed, a second rotating body and a second rotating body are disposed so as to be in pressure contact with the first rotating body and in contact with the surface on which the image of the sheet is formed. A plurality of ribs that are continuous in the circumferential direction on the outer circumferential surface of the second rotating body that conveys the sheet with the sheet sandwiched between the outer circumferential surface of the first rotating body and spaced apart in the axial direction. and, wherein the plurality of ribs contact width 6 00Myuemu hereinafter the seat, or less 1000μm in the spacing between adjacent ribs 200μm or more, the axis of the ribs diameter of adjacent ribs is equal to or adjacent direction of the central portion towards the small diameter of said axial direction both side ribs of the ribs the adjacent than the diameter of the ribs, the ribs and located in front Symbol axial direction end portions than the other ribs It is characterized by being formed to have a smaller diameter Is.

According to another aspect of the present invention, in a sheet conveying apparatus that conveys a sheet on which an image has been formed, the first rotating body is disposed so as to be in pressure contact with the first rotating body and to be in contact with the surface on which the image of the sheet is formed. A rib that is continuous in the circumferential direction on the outer circumferential surface of the second rotating body that conveys the sheet sandwiched between the outer circumferential surface of the first rotating body and the axial direction in the axial direction. forming a plurality of said plurality of ribs contact width between the sheet 6 00Myuemu less, not more than 1000μm in the spacing between adjacent ribs 200μm or more, axially ribs diameter of adjacent ribs is equal to or adjacent The ribs on both ends in the axial direction are smaller in diameter than the ribs on the center side, and the height difference between adjacent ribs is 0 μm or more and 60 μm or less, and the center of the second rotating body Height of the ribs at both ends and the ribs at both axial ends The difference is characterized in that at 210μm or less 20μm or more.

  As in the present invention, by forming a plurality of circumferentially continuous ribs on the circumferential surface of the second rotating body in the axial direction, the sheet is conveyed reliably at low cost and without degrading the image quality. be able to.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a laser beam printer which is an example of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a laser beam printer, and 1A denotes a laser beam printer main body (hereinafter referred to as a printer main body).

  A laser scanner 2 is disposed above the printer main body 1A, and an image forming unit 1B is disposed below the laser scanner 2. In this embodiment, the image forming unit 1B forms an image by an electrophotographic method, and four image forming units for forming yellow, magenta M, cyan C, and black K toner images. 3 (3Y, 3M, 3C, 3K) are arranged.

  Here, each image forming unit 3 has the same configuration except that the color of the toner is different. The photosensitive drum 4a is uniformly charged by a charging unit (not shown), and the laser scanner 2 responds to the image signal. An electrostatic latent image is formed by irradiating the light. The electrostatic latent image is visualized by developing the toner with the developing device 4b.

  Endless intermediate transfer belts 5 are rotatably contacted with the respective photosensitive drums 4a, and the toner images formed on the respective photosensitive drums 4a are transferred onto the intermediate transfer belts 5 as described above. As a result, a color image is formed.

  A sheet feeding unit 1 </ b> C having a feeding roller 7 that feeds the sheets stored in the sheet cassette 6 is disposed below the printer main body 1 </ b> A. In the sheet feeding unit 1C, the sheet accommodated in the sheet cassette 6 is fed by the feeding roller 7 so that the sheet is synchronized with the formation of the toner image and the nip portion between the secondary transfer roller 8 and the intermediate transfer belt 5. Is fed to the secondary transfer portion.

  Note that the toner image on the intermediate transfer belt 5 is transferred to the sheet fed to the secondary transfer unit in this way in the secondary transfer unit. Further, the sheet onto which the toner image has been transferred is conveyed to a fixing device B positioned above, where the transferred toner image is fixed on the sheet by heating and pressing the sheet. . Thereafter, the sheet on which the toner image is fixed by heat is discharged to the discharge tray 9.

  In this fixing device B, as shown in FIG. 2, a pressure roller 21 is pressed against a rotatable fixing film 20 supported by a support member (not shown) to constitute a fixing portion B1. The fixing film 20 is heated by a heater (not shown), and when the sheet passes through the nip portion N with the pressure roller 21, the unfixed toner image formed on the sheet is heated and pressed.

  Further, as shown in FIG. 2, on the downstream side in the sheet conveyance direction of the fixing unit B1, a discharge roller 22 constituting the sheet conveyance device B2 that conveys the sheet to discharge the sheet on which the toner image is fixed to the discharge tray 9; A discharge roller 23 that is in pressure contact with the discharge roller 22 is disposed. Here, the discharge roller (conveyance roller) 22 as the first rotating body is driven to rotate by a drive source (not shown) and is provided coaxially with the roller shaft 22d and is formed of heat-resistant rubber. The discharge roller rubber 22a is provided.

  On the other hand, the discharge roller 23 is urged by an urging means (not shown) and is pressed against the discharge roller rubber 22a, and is rotated following the rotation of the discharge roller 22. The discharge roller 23 guides the sheet. It is rotatably attached to the conveyance guide 24 shown in FIG. The sheet on which the toner image is fixed by the fixing unit is conveyed while being sandwiched between the discharge roller 22 and the discharge roller 23 while the discharge roller (conveyance roller) 23 as the second rotating body is in contact with the toner image forming surface. (Discharged).

  By the way, in order to seat the discharge sheet for the purpose of curling and improving the stackability, as shown in FIG. 3, a center rib 22b as a seating member is provided at the center of the roller shaft 22d, and the center rib 22b is also provided. Discharge roller rings 22c, which are seating members, are provided on both sides. The discharge roller rubber 22a is disposed between the central rib 22b and the discharge roller ring 22c. Further, discharge waist rollers 25, which are waist members, are in pressure contact with both axial ends of the roller shaft 22d.

  Here, in this embodiment, the discharge roller central rib 22b is located between the discharge roller rubbers 22a. Further, the outer diameters of the discharge roller central rib 22b and the discharge roller ring 22c are formed larger than the outer diameter of the discharge roller rubber 23a in order to seat the sheet. And by comprising in this way, when pinching and conveying with the discharge roller 22 and the discharge roller 23, the shape of a sheet | seat becomes a curvilinear shape which waves in an axial direction like FIG. In particular, in the vicinity of the discharge roller 23, the discharged sheet has a substantially R shape.

  Next, the configuration of the discharge roller 23 according to the present embodiment will be described. As shown in FIG. 4, the discharge roller 23 has a roller body 23b, which is formed of engineering plastic or the like and is fixed to a rotating shaft 23a. The roller body 23b has a drum shape with an outer diameter decreasing from the center toward both ends in the axial direction.

  A plurality of ring-shaped minute ribs 23c continuous in the circumferential direction are formed on the circumferential surface of the roller body 23b in the axial direction with a predetermined interval. The interval between the minute ribs 23c will be described later.

  Here, as shown in FIG. 5, the diameters of the minute ribs 23c are gradually reduced from the center side toward both ends so as to follow the drum shape of the roller body 23b. Further, as described above, the curve connecting the apexes of the minute ribs 23c is uniformly in contact with the sheet having a substantially R shape in the vicinity of the discharge roller 23 when being nipped and conveyed by the discharge roller 22 and the discharge roller 23. Thus, it has an R shape similar to the shape when the sheet is discharged.

  In the present embodiment, the number of the minute ribs 23c is set to ten. However, the number of the minute ribs 23c is not particularly limited, and when the sheet is discharged such that the minute ribs 23c uniformly contact the sheet. Any number can be used as long as the shape is similar to the shape. Of course, if there are conditions, the number of the ribs can be further increased. In this way, the number of the minute ribs 23c is increased, which is more preferable because the pressing force to the sheet can be dispersed.

  In the present embodiment, the outer peripheral surface of the minute rib 23c is formed to coincide with the outer peripheral surface of the roller body 23b. That is, in the present embodiment, the circumferential surface of the roller body 23b is shaped so that the sheet pressed by the central rib 22b and the discharge roller ring 22c and the like, and the sheet on the circumferential surface of the roller body 23b The contact surface is constituted by a plurality of minute ribs 23c. Further, the minute ribs 23c are formed integrally with the roller body 23b, and a POM having a high slidability is used as a member. Note that the minute ribs 23c and the roller body 23b may be formed of separate members.

  Further, the top of the minute rib 23c in the present embodiment is formed in a flat shape as shown in FIG. However, this top part may be formed in a curved shape, and when the top part of the minute rib is flat, its edge may or may not be chamfered in the R shape.

  Next, each parameter of the minute rib 23c in the present embodiment will be described. As shown in FIG. 5, the parameters of the minute ribs 23c include the contact width S of the individual minute ribs 23c to the sheet, the interval (pitch) P between adjacent minute ribs, and the height H of the groove of the minute ribs 23c. Is mentioned. Further, the height difference ΔH1 to ΔH4 between the adjacent minute ribs 23c, the height difference D between the minute ribs 23c at the center of the discharge roller 23 and the minute ribs 23c at both ends, and the curvature r of the curve connecting the vertices of the minute ribs 23c. Can be mentioned.

  In the present embodiment, the contact width (contact width) S of each minute rib 23c to the sheet is a straight line parallel to the axial direction 0.2 mm lower than the apex of the minute rib 23c, as shown in FIG. And the distance between the intersections of the curve forming the microribs. Here, the distance of 0.2 mm is determined by the amount of biting of the minute ribs 23c into the sheet being about 0.2 mm at the maximum.

  In the present embodiment, the contact width S of the individual microribs 23c to the sheet is about 400 μm, the interval P between adjacent microribs is about 700 μm, and the height H of the microribs 23c with the groove is 200 μm. Degree. Further, the height difference ΔH1 to ΔH4 between the adjacent minute ribs 23c is about 20 μm, and the height difference D between the minute ribs 23c at the center and the minute ribs 23c at both ends is about 110 μm, and a curve connecting the vertices of the minute ribs 23c. The curvature r is about R45.

  Next, the limit value of each parameter of the minute rib 23c obtained experimentally will be described. FIG. 7 is an image evaluation of the toner image that is heated and fixed by the fixing unit and is nipped and conveyed by the discharge roller 22 and the discharge roller 23 when each parameter of the minute rib 23c is changed. In the image evaluation shown in FIG. 7, “◯” indicates that there is no occurrence of image quality deterioration, and “×” indicates that there is image quality reduction, based on visual judgment. Based on the results shown in FIG. 7, the limit values of the parameters of the minute rib 23c will be described.

  First, the contact width of the minute ribs 23c to the sheet will be described. When the contact width S is larger than 600 μm, the width of the portion where the surface property of the toner image fixed on the sheet by the individual minute ribs 23c changes is widened. As a result, deterioration in image quality due to the roller marks generated by the minute ribs 23c cannot be sufficiently suppressed.

  On the other hand, if the contact width S of the individual minute ribs 23c to the sheet is 600 μm or less, the width of the portion where the surface property of the toner image changes is sufficiently narrow, so that deterioration in image quality can be suppressed. Accordingly, the sheet contact width S of the minute ribs 23c is preferably set to a predetermined value of 600 μm or less.

  Next, the interval between the minute ribs 23c will be described. When the interval P between the adjacent minute ribs 23c is 200 μm or less, the interval between the portions where the surface property of the toner image fixed on the sheet by the individual minute ribs 23c changes is also narrowed. For this reason, as a result, it approaches the same state as a flat shape without ribs, and deterioration in image quality due to roller marks cannot be suppressed. Further, when the interval P between the adjacent minute ribs 23c is 200 μm or less, it becomes difficult to mold the mold of the discharge roller 23 in the resin material, so that mass productivity cannot be secured.

  On the other hand, when the interval P between the adjacent minute ribs 23c is larger than 1000 μm, the interval between the portions where the surface property of the toner image fixed on the sheet by the individual minute ribs 23c changes becomes too large. For this reason, a portion where the surface property of the toner image changes and a portion where the surface property does not change can be visually recognized.

  Further, when the interval P between the adjacent minute ribs 23c is larger than 1000 μm, the number of the minute ribs 23c decreases if the pressure contact length of the discharge roller 23 to the discharge roller 22 in the rotation axis direction is maintained at a predetermined length. The sheet conveying force is reduced. In this case, if the pressing force of the discharge roller 23 to the discharge roller 22 is increased in order to maintain the conveyance force, deterioration in image quality due to roller marks, toner removal, or the like cannot be suppressed.

  On the other hand, when the interval P between the adjacent minute ribs 23c is 200 μm or more and 1000 μm or less, it is not necessary to increase the sheet conveying force, so that deterioration in image quality can be suppressed. Therefore, it is preferable to set the interval P between adjacent minute ribs to a predetermined value in the range of 200 μm to 1000 μm.

  Next, the height of the minute rib 23c with the groove will be described. When the height H with respect to the groove of the minute rib 23c is lower than 100 μm, the concave portion of the minute rib 23c becomes closer to the sheet, so that the heat of the toner image fixed on the sheet is taken away also in the concave portion. For this reason, roller marks are generated and image quality is degraded.

  On the other hand, when the height H with respect to the groove of the minute ribs is higher than 300 μm, it is difficult to mold the discharge roller 23 in the resin material that maintains the interval between the adjacent minute ribs in the predetermined range. For this reason, the mass productivity of the discharge roller 23 cannot be ensured. Therefore, the height of the minute rib 23c with the groove is preferably set to a predetermined value in the range of 100 μm to 300 μm.

  Next, the height difference between adjacent minute ribs 23c will be described. When the height differences ΔH1 to ΔH4 between the adjacent minute ribs 23c are less than 0 μm, that is, the height relationship with the grooves of the minute ribs 23c is gradually decreased from the central portion toward both ends of the discharge roller 23, and the height relationship is reversed. In this case, minute ribs 23c that do not hit the sheet are generated. For this reason, the small ribs 23c that are in contact with the sheet locally apply a high pressure to the sheet, and the image quality is deteriorated due to the removal of toner and the occurrence of unevenness of the sheet.

On the other hand, when the height differences ΔH1 to ΔH4 between the adjacent minute ribs 23c are larger than 60 μm, the variation in the height H of the minute ribs 23c increases, and the minute ribs 23c that do not hit the sheet are generated. For this reason, as in the case where the height difference ΔH between the adjacent minute ribs 23c is less than 0 μm, the image quality is deteriorated due to the removal of the toner and the occurrence of the unevenness of the sheet.
Therefore, the height differences ΔH1 to ΔH4 between the adjacent minute ribs 23c are preferably set to a predetermined value in the range of 0 μm to 60 μm.

  Next, the difference in height between the minute ribs at the center and both ends of the discharge roller 23 will be described. When the height difference D between the central rib of the discharge roller 23 and the minute ribs at both ends is smaller than 20 μm, the minute ribs at both ends of the discharge roller 23 are strong against the sheet when the posture of the sheet or the discharge roller 23 is inclined. Hit it. For this reason, the toner is peeled off at the minute ribs at both ends of the discharge roller 23, or the sheet is uneven, and the image quality is deteriorated due to the unevenness of the sheet.

  On the other hand, when the height difference D between the rib at the center of the discharge roller 23 and the minute ribs at both ends is greater than 210 μm, the curvature of the curve connecting the vertices of the minute ribs 23c becomes smaller, and the rib at the center of the discharge roller 23 becomes smaller. Strongly hits the sheet. For this reason, the unevenness | corrugation of the same shape as the curve shape which connected the vertex of each minute rib 23c generate | occur | produces on a sheet | seat, and the fall of image quality will generate | occur | produce by generation | occurrence | production of this unevenness | corrugation of a sheet | seat. Therefore, the height difference D between the central rib of the discharge roller 23 and the minute ribs at both ends is preferably set to a predetermined value in the range of 20 μm to 210 μm.

  Next, the correlation between parameters of the minute rib 23c will be described.

  First, the contact width S of the individual minute ribs 23c to the sheet does not correlate with other parameters. This is because whether the width of the portion where the surface property of the toner image changes is sufficiently narrow depends only on the contact width S of the minute ribs 23c to the sheet.

  Further, the height H of the minute rib 23c with the groove does not correlate with other parameters. This is because whether or not the heat of the toner image fixed on the sheet is removed even in the concave portion of the minute rib 23c depends only on the height H with respect to the groove of the minute rib 23c. Further, when the height H of the micro ribs is higher than 300 μm, in the resin material that maintains the interval P between the adjacent micro ribs within the predetermined range, the mold of the discharge roller 23 is formed regardless of other parameters. Will be difficult.

  On the other hand, the interval P between adjacent minute ribs, the height difference ΔH1 to ΔH4 between adjacent minute ribs 23c, and the height difference D between the central rib and the minute ribs at both ends of the discharge roller 23 are correlated with the image quality evaluation. There is. FIG. 8 shows the height differences ΔH1 to ΔH4 of the adjacent microribs 23c and the height difference D of the microribs at the center and both ends of the discharge roller 23 when the spacing P between the adjacent microribs is 200 μm, 700 μm, and 1000 μm, respectively. The image quality evaluation when changed is shown. Further, in the image evaluation shown in FIG. 8, “目視” indicates a particularly optimal condition, “◯” indicates no occurrence of deterioration in image quality, and “×” indicates occurrence of deterioration in image quality, based on visual judgment.

  As can be seen from the results of FIG. 8, when the interval P between adjacent microribs is 200 μm, the image quality deteriorates when the height difference D between the microribs at the center of the discharge roller 23 and the microribs at both ends is 210 μm or more. Occurs.

  This is because if the spacing between adjacent microribs is narrow, the curvature of the curve connecting the vertices of each microrib becomes too small just by slightly increasing the height difference between the center rib and the microribs at both ends of the discharge roller. Because it will end up. If the curvature of the curve becomes too small in this way, irregularities having a curved shape connecting the vertices of the minute ribs are generated on the sheet, and the image quality is deteriorated.

  In addition, when the interval P between adjacent minute ribs is 1000 μm, the image quality deteriorates when the height difference D between the minute ribs at the center and both ends of the discharge roller is less than 110 μm. This is because, when the interval between adjacent microribs is wide, the microribs at both ends of the discharge roller strongly hit the sheet unless the height difference between the central ribs of the discharge roller 23 and the microribs at both ends is increased. . Furthermore, even when the distance P between adjacent microribs is 1000 μm and the height difference ΔH1 to ΔH4 between adjacent microribs is less than 20 μm, the height difference between the microribs at the center and both ends of the discharge roller 23 cannot be increased. Therefore, the image quality is degraded.

  In addition, when the height difference ΔH1 to ΔH4 between adjacent minute ribs is less than 20 μm, if the height difference D between the minute ribs at the center and both ends of the discharge roller is 210 μm or more, it does not depend on the distance P between the adjacent minute ribs. The height difference between the small ribs at the center and both ends of the discharge roller cannot be increased. For this reason, the image quality is degraded.

  On the other hand, when the interval P between adjacent minute ribs is 700 μm, each parameter of the minute ribs can be widely adopted, which can be said to be optimal. In particular, the interval P between adjacent microribs is about 700 μm, the height difference D between the microribs at the center and both ends of the discharge roller is about 110 μm, and the height differences ΔH1 to ΔH4 between adjacent microribs are about 20 μm. It is best to be.

  As described above, in this embodiment, when the sheet is seated, the sheet is sandwiched between the discharge roller 22 and the discharge roller 23 when the sheet is bent by being pressed by the central rib 22b or the discharge roller ring 22c. The part has a curved shape as shown in FIG. Then, the shape of the discharge roller 23 is reduced from the central portion toward both ends in the axial direction so as to follow the curved shape of the sheet, and continuous with the circumferential surface of the discharge roller 23 in the circumferential direction. A plurality of the minute ribs 23c are formed in the axial direction. As described above, when seating is performed, the curved shape (deflection shape) of the seat by seating may be a shape that follows the shape of the discharge roller 23.

  That is, in the present embodiment, the discharge roller 23 is formed so that the diameter decreases from the central portion toward both ends in the axial direction, and the minute ribs 23c continuous in the circumferential direction on the circumferential surface of the discharge roller 23. Are formed in the axial direction. Thus, the sheet is discharged while the minute ribs 23c are in line contact with the sheet while maintaining the conveying force required for the sheet, so that the amount of heat taken by the discharge roller 23 from the sheet can be minimized.

  In the present embodiment, the form in which the sheet is seated by the central rib 22b or the discharge roller ring 22c is exemplified. However, even when the seating is not performed, if the shape of the discharge roller 23 in contact with the surface on which the image of the sheet is formed is as described above, it is possible to prevent deterioration in image quality.

  Further, since the minute ribs 23c are not uneven in the sheet discharging direction, the portion where the surface property of the toner image fixed on the sheet changes due to contact can be made inconspicuous without impairing the releasability. Further, by forming the minute ribs 23c so that the diameter decreases from the central portion of the discharge roller 23 toward both ends in the axial direction, the generation of local high pressure is suppressed even when the contact area is reduced. . As a result, it is possible to suppress occurrence of roller marks, image peeling, and sheet unevenness at a lower cost than in the past.

  In this way, by forming a plurality of circumferentially continuous fine ribs 23c on the circumferential surface of the discharge roller 23 in the axial direction, the sheet can be discharged reliably at low cost and without degrading the image quality. Can do.

  Next, a second embodiment of the present invention will be described.

  FIG. 9 is a diagram illustrating a discharge roller provided in the sheet conveying apparatus according to the present embodiment. In FIG. 9, the same reference numerals as those in FIG. 5 described above indicate the same or corresponding parts.

  Here, the number of the minute ribs 23c in the present embodiment is ten as shown in FIG. The outer diameters of the six minute ribs 23c at the central portion of the paper discharge roller 23 are the same, and the outer diameters of the four minute ribs 23c located at both ends become smaller toward the end in the axial direction. ing.

  In such a configuration, the height differences ΔH1 and ΔH2 of the adjacent minute ribs 23c at the center of the paper discharge roller 23 are approximately 0 μm. Here, it is preferable that ΔH1 and ΔH2 are formed to be 20 μm or less because there is no deterioration in image quality. By forming ΔH1 and ΔH2 to be 20 μm or less, it is possible to prevent the generation of minute ribs 23c that do not hit the sheet, and it is possible to prevent a high pressure from being locally applied to the sheet. Because.

  The relationship between ΔH3 and ΔH4 and image evaluation is the same as that in the first embodiment described above. Further, the contact width S of the minute ribs 23c to the sheet, the interval P between adjacent minute ribs, the height H of the minute ribs 23c, the height difference D between the minute ribs at the center and both ends of the discharge roller 23, etc. The relationship between each parameter of the minute rib 23c and the image evaluation is also the same as in the first embodiment described above.

  As described above, by aligning the outer diameters of the six minute ribs in the central portion of the paper discharge roller 23, the pressing force against the sheet 11 can be reliably ensured in the central portion of the paper discharge roller 23. Further, the four minute ribs 23c located at both axial ends of the paper discharge roller 23 are formed so that the diameter decreases toward the axial end, so that the first embodiment described above is performed. Similar to the form, the shape of the minute ribs 23c can be similar to the shape of the discharged sheet.

  As a result, it is possible to obtain a conveying force necessary for conveying the sheet 11 and to make a portion where the surface property of the toner image fixed on the sheet 11 changes due to contact with the discharge roller 23 less noticeable. .

  Heretofore, a full-color laser beam printer has been described as an example of the image forming apparatus. However, the present invention is not limited to this, and may be a monochrome printer. It can also be applied to an image forming apparatus. Further, the case where the minute rib is formed on the discharge roller 23 has been described so far. However, the present invention is not limited to this, and the minute rib 23c may be formed on at least one of the discharge roller 23 and the discharge roller rubber 22a. good. Further, until now, the minute ribs 23c are formed in a ring shape, but the minute ribs 23c may be formed in a screw shape.

1 is a diagram illustrating a configuration of a laser beam printer which is an example of an image forming apparatus according to a first embodiment of the present invention. 2 is a diagram illustrating a configuration of a fixing device provided in the laser beam printer. FIG. 2 is a diagram illustrating a configuration of a sheet conveying device provided in the fixing device. FIG. The perspective view of the discharge roller which comprises the said sheet conveying apparatus. The surrounding surface expanded sectional view of the said discharge roller. The figure explaining the sheet contact width of the microrib provided in the said discharge roller. The chart which shows image evaluation of a toner image when each parameter of the above-mentioned minute rib is changed. The chart which shows the correlation of each parameter of the above-mentioned minute rib. The figure explaining the discharge roller provided in the sheet conveying apparatus which concerns on the 2nd Embodiment of this invention. The figure explaining the structure of the conventional sheet conveying apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser beam printer 1A Laser beam printer main body 1B Image formation part 22 Discharge roller 22a Discharge roller rubber | gum 22b Central rib 22c Discharge roller ring 22d Roller shaft 23 Discharge roller 23b Roll body 23c Minute rib 25 Discharge waist roller 11 Sheet B Fixing device B1 Fix Part B2 Sheet conveying device

Claims (9)

In a sheet conveying apparatus that conveys a sheet on which an image is formed,
A first rotating body;
A second rotator that is pressed against the first rotator and disposed so as to contact a surface on which an image of the sheet is formed, and
A plurality of ribs continuous in the circumferential direction are formed on the outer circumferential surface of the second rotating body that conveys the sheet with the outer circumferential surface of the first rotating body sandwiched between them, and are formed in the axial direction.
Wherein the plurality of ribs contact width 6 00Myuemu hereinafter the seat, or less 1000μm in the spacing between adjacent ribs 200μm or more, in the axial direction of the ribs diameter of adjacent ribs is equal to or adjacent smaller towards the diameter of said axial direction both side ribs of the ribs the adjacent than the diameter of the central ribs, the ribs and located in front Symbol axial end portions, is diameter than the other ribs A sheet conveying apparatus, wherein the sheet conveying apparatus is formed to be small. In a sheet conveying apparatus that conveys a sheet on which an image is formed,
A first rotating body;
A second rotator that is pressed against the first rotator and disposed so as to contact a surface on which an image of the sheet is formed, and
A plurality of ribs continuous in the circumferential direction are formed in the circumferential direction on the outer circumferential surface of the second rotating body that conveys the sheet with the outer circumferential surface of the first rotating body,
Wherein the plurality of ribs, contact width between the sheet 6 00Myuemu less, not more than 1000μm in the spacing between adjacent ribs 200μm or more, the central portion side in the axial direction in rib diameter of adjacent ribs is equal to or adjacent The ribs on both ends in the axial direction are smaller in diameter than the ribs of each of the ribs, and the height difference between adjacent ribs is 0 μm or more and 60 μm or less, A sheet conveying apparatus, wherein a height difference between ribs at both ends in an axial direction is 20 μm or more and 210 μm or less. The first rotating body is positioned between the plurality of rotating body main bodies and the plurality of rotating body main bodies, and presses and seats the sheet nipped and conveyed by the rotating body main body and the second rotating body. With a seating member,
The second rotating body has a shape that decreases in diameter from the central portion toward both ends in the axial direction so as to follow the shape of the sheet that is pressed and bent by the seating member, and the sheet of the circumferential surface The sheet conveying apparatus according to claim 1, wherein the contact surface includes a plurality of the ribs.   With respect to each of the plurality of ribs, the diameter of the ribs on both axial sides of the adjacent ribs is smaller than the diameter of the ribs on the central portion side in the axial direction among the adjacent ribs. The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is set. Among previous SL plurality of ribs, the sheet conveying device according to any one of claims 1 to 3, characterized in that the diameter of the rib adjacent is placed in the center of the axial direction are equal.   The rib has a height of 100 μm or more and 300 μm or less, a height difference between adjacent ribs of 0 μm or more and 60 μm or less, and a height difference between the rib at the center of the second rotating body and the ribs at both ends in the axial direction is 20 μm or more. The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is 210 μm or less.   The sheet conveying apparatus according to claim 1, wherein the plurality of ribs have a height of 100 μm or more and 300 μm or less.   An image forming apparatus comprising: an image forming unit; and a sheet conveying device according to claim 1 for conveying a sheet on which an image is formed by the image forming unit.   9. The image forming apparatus according to claim 8, wherein the sheet conveying device is provided on a downstream side of a fixing unit that fixes the toner image formed by the image forming unit to the sheet by heat.

Images